1. Field of the Invention
This invention relates to an improved photoconductor of the cadmium sulfide/cadmium carbonate type and a method for making same. The photoconductor is typically set in an organic binder and is useful in both toner transfer and charge transfer electrophotography.
2. Description of the Prior Art
Numerous patents and other publications have disclosed methods for making photoconductors of the cadmium sulfide/cadmium carbonate type dispersed in an organic binder, such as U.S. Pat. Nos. 3,494,789; 3,506,595; 3,541,028; 3,589,928; 3,615,401; 3,704,123 and 3,867,139.
U.S. patent application Ser. No. 501,566, filed Aug. 29, 1974, commonly assigned with the present invention, teaches the importance of keeping ionic contaminants out of the end product and discloses methods for removing these ionic contaminants and assuring that they stay removed. That application discloses that:
(1) in lieu of cadmium sulfide, one may use cadmium selenide or a mixture of cadmium sulfide and cadmium selenide; PA1 (2) a useful range for the amount of cadmium carbonate is between zero and four moles cadmium carbonate per mole of cadmium sulfide, cadmium selenide, or mixture thereof; PA1 (3) the ionic contaminants from which the resultant end product is free are the group consisting of sodium, chlorine, bromine, potassium, and nitrate; and PA1 (4) the photoconductor is activated with a dopant selected from the group consisting of copper chloride, silver chloride, copper sulfate, silver sulfate, copper nitrate, silver nitrate, copper ammonia complex, silver ammonia complex, copper carbonate dissolved in ammonia, and silver carbonate dissolved in ammonia. PA1 1. The photographic speeds are not sufficiently high for some applications, e.g., in copiers in which a high throughput rate is desired and/or the amount of light available for exposure is limited. PA1 2. Along with low speeds, one frequently encounters a "memory effect". For example, some copying machines using a cylinder coated with a photoconductive layer made according to the prior art may involve more than one complete cylinder revolution for producing each copy, and an undesired "ghost" image may be superimposed on the desired image. With faster photoconductors, residual charge is discharged more completely using an erasing light, and ghost images do not appear as readily. PA1 3. At high humidities, a slight but definite degradation of the electrophotographic properties, particularly the charge acceptance, is observed. It is possible that, under the photoconductive power calcination conditions and procedures taught by the prior art, a small residue of ionic substances, even though not readily detected by analysis, may be present.
U.S. patent application Ser. No. 715,804 filed Aug. 19, 1976, and commonly assigned with the present invention, teaches that the calcination in an inert atmosphere such as nitrogen gas rather than air is a good safeguard for preventing the introduction of unwanted ionic contamination, particularly that of the sulfate ion.
Electrophotographic plates fabricated by the teachings of the prior art suffer, however, from certain limitations. Among these are the following:
These and other drawbacks of the prior art are remedied by the present invention, some of the objects of which are as follows: